How Cities Stress Us Out

Below:

Next story in Science

Full of blaring horns, flashy billboards and fast-talking
residents, cities can be stressful places to be.

So, it may be no wonder that urban-dwellers suffer from higher
rates of schizophrenia, depression and other mental health
problems, compared to people who live in quieter places.

Now, a new study helps explain why cities stress us out, and the
answer seems to lie in our brains.

In stressful social situations, the study found, people who live
in cities showed extra activity in a brain area that is
associated with depression, anxiety and even violence. People who
live in rural areas but were born in cities showed a similar kind
of brain hyperactivity, the study found, suggesting that your
place of birth may forever affect the way you deal with stress.

The researchers don't recommend that urbanites run out to sell
their condos in favor of country homes. After all, there are
plenty of reasons why living in a city can be good for both
mental and physical health, including a plethora of stimulating
environments and easier access to good health care.

Instead, the findings offer researchers and urban planners a new
way to figure out what it is about cities that induce anxiety.
And that, in turn, could help in designing cities that can reduce
-- instead of invoke -- stress.

"We're not like Jane Austen, saying that cities are bad and
countries are great," said lead researcher Andreas
Meyer-Lindenberg, a psychiatrist at the University of
Heidelberg's Central Institute of Mental Health in Mannheim,
Germany. "It's not black and white."

"The thing is that it was known before that cities are a risk
factor for mental health," he added. "What we show is how and
what underlies that in the brain."

People who are born or brought up in cities are twice as likely
to be schizophrenic as people born into more relaxing settings,
according to previous work. The risk for anxiety is 20 percent
higher for city-dwellers. And their risk for depression and other
mood disorders is nearly 40 percent higher.

To test the biology behind those trends, Meyer-Lindenberg and
colleagues challenged dozens of people to solve a series of
difficult math problems under time pressure. An adaptive computer
program that produced harder problems in response to correct
answers ensured that participants could answer only about a third
of the questions correctly.

All the while, participants were shown performance meters, which
essentially told them: "You're the worst person ever in our lab
to do this task," Meyer-Lindenberg said.

But that's not all. "We'd come in between rounds and criticize
them. We'd say, 'We know this is difficult for you, but you know,
this is important and expensive. Please try harder.'"

Measurements of stress hormones, blood pressure and heart rate
confirmed that participants were, indeed, stressed out by the
task. More revealing were brain scans taken by fMRI machines.

A part of the brain called the amygdala, which is involved in
anxiety, depression and the fight-or-flight response, was extra
active in people who were from cities, the researchers report
today in the journalNature. What's more, that level of
activity went up with the size of the city they were from.

"What we show is that if you live in a city, those brain areas
that are linked to mental illness are hyperactive,"
Meyer-Lindenberg said.

Future brain-scanning studies should help scientists figure out
whether it's noise, pollution, over-stimulation or other factors
that give cities such influence over our brains.

"It might be the number of times you encounter strangers or it
might have to do with visual stimuli, like billboards," said Dan
Kennedy, a neuroscientist at the California Institute of
Technology in Pasadena. "We don't have a precise explanation for
these effects. But it opens up a new area for research."

More than half of people on Earth now live in cities, and that
number is expected to be close to 70 percent by 2050. Reversing
those demographic trends is unrealistic. What is possible,
suggests the new research, is constructing cities that are
healthier for people to live in.

"Humans are now living in environments we really didn't evolve
in, and our brains might not be perfectly tuned to these new
environments," Kennedy said. "We're facing pressures and
situations that our species may have never encountered in the
past. I think that's just something we have to keep in mind
moving forward as cities develop."